Process for the preparation of products from lignin by hydrogenation



the hydrogenation.

Patented Dec. 4, 1945 PROCESS FOR THE PREPARATION OF PROD- UCTS FROMLIGNIN B Y HYDROGENA- TION Karl Freudenberg and Willy Lautsch,Heidelberg, Germany; vested in the Alien Property Custodian No Drawing.Original application July 29, 1940,

Serial No.

tion September 19, 1940 Germany July 29, 19

348,07936. Divided and this applica- Serial No. 357,498. In

l 6 Claims. (Cl. 260-124) This invention relates to a process oi makingproducts from lignin by hydrogenation. The hydrogenation of lignin orlignin containing substances has been tried several times. Distillation.with zinc-dust has not lead to technical or comniercial results.Somewhat better results have been obtained by carrying out thehydrogenation with hydrogen under pressure and in the presence ofcatalysts. Thus, Fierz -David and Hennig have used a distillation inhydrogen under pres! sure in the presence of nickel and obtained amixture of rather volatile constituents and tar having a total weight ofabout 20% of the used amount of lignin. In the tarry constituents therecould be ascertained, besides acids, alcohols, diketones, furanederivatives etc., about 8% of a mixture of different phenols.

This application is a division of our application S. N. 343,079 filedJuly 29, 1940.

Another mode of operation differing somewhat from the aforementionedprocesses has been tried by Harris, DJanni and Adkins (see JournalAmerican Chemical Society 60, 1467, 1938), who have dissolved the ligninor lignin constituentswhich for the greatest part are insoluble inwater-in alcohol in the presence of mineral acids and carried out thehydrogenation in organic solvents under pressure, using the oxides ofchrome and copper as catalyst. In this case there had been obtainedmainly hydro-aromatic alcohols, that is derivatives of thecyclo-hexylpropane. This process requires a preliminary treatment of thelignin with an alcoholic mineral acid and results, especially-in case ofconifers, in a solution of only a part of the lignin r ligninconstituents. Besides. hydrogenation is carried outin such caseinorganic solvents, for instance dioxane. Owing to these necessities,however, the obtained product is but of limited commercial use. Now, wehave found that the catalyst used by these inventors is not wellsuitable for the present process which is destined for the production ofother products.

More particularly, we have found that essentially more favorable resultsmay be attained by carrying out the hydrogenation with hydrogen underpressure in the presence of a suitable catalyst in an aqueous, alkalinemedium. In this case the dissolving and splitting action of dilute hotalkali will come into efiect simultaneously with Accordingly, the 1process may be carried out with greater uniformity in an aqueoussolution or suspension. It is a surprising fact that with our newprocess more than one half of the lignin of the form of phenols orphenol derivatives may be converted into a condition permittingdissolution in ether. Heretofore this could not be attained with anyknown process of hydrogenating lignin. In addition, our new process isconnected with the important advantage, that it may be successfullyapplied to wood substance as well as to isolated lignins or ligninderivatives, such as lignin sulphoacid, sulphite cellulose waste lye,black lye and the like.

Example 1 300 g. of ciiproxam-lignin (obtained from wood-flour or thelike by extraction and treatment with copper oxide and ammonia), aremixed with 3 liters of a 10% nickel sulphate solution whereupon themixture is heated to boiling tem- .perature and dilute sodium lye addedby drops to with constant stirring, until the temperature after abouttwo hours assumes a value of 260 C. The pressure thus generated in theautoclave will be about within 190 and 210 atmospheres,superatmospheric. The mixture is left standing for about two hours atthe stated temperature.

on cooling the mass is removed from the nickel catalyst by filtering,preferably with exclusion of air, washed again slightly and the alkalinefiltrate treated with carbonic 'acid under pressure in order to liberatethe phenols. The solution which contains mainly pyrocatechin, guajacol,creosol as well as their higher homologues may either be subjected tofurther treatment or the phenols may be obtained therefrom in knownmanner, for instance by extraction and fractional distillation.

0n thorough shaking of the solution with ether or another suitablesolvent and evaporation of the solvent there is obtained a residue ofphenol in an amount of about 180 g., corresponding to 60% of the usedlignin. About one half of this residue consisting of approximately evenproportions of pyrocatechin, guajacol and their homologues may bedistilled and the constituents isolated in pure conditionby means ofdistillation in high vacuum and fractionation (for instance in f theWidmer spiral).

. autoclave.

Example 2 300 g. of lignin, isolated by means of a mixture ofhydrochloric acid and phosphoric acid are stirred with 3 liters of anickel sulphate solution and the nickel precipitated as a carbonate onthe lignin with dilute solution of soda. The residue on being removed bysuction and washed is slurried with 3 liters of water and mixed with 160g. of solid caustic soda. The mixture is there'- upon subjected tohydrogenation under pressure carried out under the same conditions as inExample 1. Isolation of the phenols is likewise conducted in the mannerstated in Example 1. The yield is also the same as given in thisexample.

Example 3 The mode of operation is the same as in Example 1, thediiference being only that palladium is used as a catalyst. Palladium isprecipitated on the lignin as metal by reduction with formaldehyde.Hydrogenation under pressure, mode of working as well as the yieldsareapproximately the same as in Example 1.

Example 4 6 liters of sulphite cellulose waste lye containmg 240 g. oflignin are neutralized with sodium lye and, in addition, mixed with anexcess of 100 g. solid caustic soda. This solution is mixed with acomposite catalyst consisting of nickel sulphide, iron sulphide andactivated carbon. This catalyst had been prepared by adding 100 g. ofactivated carbon to a solution of 60 g. of nickel sulphate, 60 g. offerrous sulphate and 150g. of sodium acetate, followed by saturationwith sulphuretted hydrogen, removal by suction and washing with water.The composite catalyst consisting of a mixture of sulphite waste lye issubjected to hydrogenation under pressure in an Similarly to Example 1,at first hydrogen is introduced until the pressure is raised to apressure of 120 atmospheres, superatmospheric and after about two hoursthe temperature is raised to 260 C. by heating. The reaction pressure at260 C. is approximately 270 atmospheres, superatmospheric. After abouteight hours the mass is cooled and saturated with carbonic acid with theresult of giving all large amounts of sulphuretted hydrogen. By workingthe mass as above stated, there will be obtained products which aresoluble in ether, that is mainly again pyrocatechin, guajacol andcreosol in an amount of about 120 g. corresponding to approximately 50%of the used lignin.

In the foregoing we have shown that lignin or substances containinglignin, including sulphite cellulose waste lye may be converted in analkaline medium in the presence of catalyst and compressed hydrogen inan amount up to 50% of the lignin constituent into products which aresoluble in either. According to the kind of catalyst used. theseproducts belong to the phenol series or to the cyclo-paraflinic alcoholsgenerated therefrom.

In further developing our invention we have found, that products whichare soluble in ether may also be obtained without the use of a cata-'lyst, when using sufllciently high temperatures and pressures duringcarrying out the process.

At temperatures of about 260 C. the proportion of phenols having ahigher molecular weight will preponderate, while the additionallyproduced cyclic alcohols belong mainly to the cyclohexane series. Alsoat 300 C. the proportion of clic alcohols with 6 members.

, smaller.

phenol is greater and the proportion of alcohols The phenols have a highboiling point and are only to a small part lignin products with but onenucleus, while the products obtained in accordance with the foregoingpart of this specification with catalysts are of a much more simplestructure and consequently may be distilled more easily. Thus, withincreasing temperature the proportion of cyclo-paraffinic alcoholslikewise increases. Increasing temperature will further cause anarrowing of the ring structure and conversion from the cyclo-hexane tothe cyclo-pentane series.

Accordingly, at a temperature of about 350 C. predominantly alcohols ofthe cyclo-hexane and cyclo-pentane series are obtained, in an amountcorresponding to 35% of the proportion of lignin. Besides, there isobtained a small amount, about 14%, of phenols. Using still highertemperatures and long reaction times the proportion of phenol willdisappear more and more in favor of the mentioned alcohols. Forinstance, if the temperature is raised above the range of 370-400 C.,the aforementioned specific lignin products will undergo further changesand approach the products obtained in the synthetic production ofbenzene.

Example 5 1000 ccm. of an aqueous solution of sodium sulphite of lignincorresponding to 11 .5 g. of lignin, on adding 60 g. of sodium hydroxideare heated to a temperature of 345-355 C. in a shaking autoclave,hydrogen being introduced under a pressure between and atmospheressuperatmospheric. The alkaline solution on cooling is well shakentogether with ether, the separated ethereal solution dried and the etherevaporated. There is obtained as residue 42-45 g. of neutralconstituents corresponding to 35-38% of the used lignin. 60% of thisamount, that is 21% of the used lignin, can be distilled in normal orhigh vacuum. The low boiling fractions comprise the cyclo-pentanol andits homologues, while the higher boiling fractions belong in part to thecy- If carbonic acid is introduced into the alkaline solution which isliberated from neutral constituents as far as to saturation of thissolution, there can be obtained by renewed extraction with ether about1'7 g. of phenolic constituents, corresponding to 14.5% of the usedlignin.

Example 6 500 ccm. of an aqueous solution of sodium sulphate of lignin,corresponding to'70.5 g. of lignin, on addition of 40 g. of sodiumbicarbonate and impression of hydrogen having a pressure of 100atmospheres, superatmospheric, are heated during four hours toatemperature between 345 and 350 C. On cooling the mass is de-etherizedand on evaporation of the "ether. there will remain 20 g. of a substancecorresponding to 28.4% of the used lignin, this substance consistingmainly of cyclic alcohols.

Example 7 550 ccm. of an aqueous solution of sodium sulphate of lignincorresponding to 28.2 g. of lignin, on addition of 17 g. of sodiumbicarbonate at an initial pressure of the introduced hydrogen of 30atmospheres, superatmospheric are heated for three hours to atemperature between 400 and 420 C. The yield of neutral constituents(cyclohexanols) amounts to 5.3 g., that is 18.8% of the used lignin.

Example 8 500 com. of an aqueous solution of sodium sulphate of lignincontaining 28.2 g. oi! lignin on addition of g. of sodium hydroxide witha pressure of the introduced hydrogen of 80 atmospheres,superatmospheric are heated for six hours to a temperature of 260 C. Themass is worked in the same manner as in Example 5. There will beobtained 1.7 g. of neutral constituents and 4.7 g. of phenolscorresponding to 6% and 16.7 respectively, of the used lignin.

The neutral constituents produced according to Examples 4 to 8 may besubsequently hydrogenated with or without a catalyst (at highertemperatures without a catalyst and with or without the use of asolvent) in order to effect complete hydrogenation and further splittingat 260-350 C. at a pressure of 80 to 100 atmospheres, superatmospheric.Up to 70% of the products obtained in this way can no more be distilled.

We claim:

1. A non-catalytic process for the hydrogenation of a material selectedfrom the group consisting of sodium salts of lignin obtained from wasteliquors of the sulphite pulp, process and sodium salts of ligninobtained from waste liquors of the sulphate pulp process, whichcomprises reacting the said material under pressure with hydrogen in anaqueous alkaline medium, at a temperature of the order of 250 C. to 420C., the introduction pressure of the hydrogen ranging from to 120atmospheres and recovering the reaction products. g 2. A non-catalyticprocess for the hydrogenation of a material selected from the groupconsisting 01 sodium salts of lignin obtained from waste liquors of thesulphite pulp process and sodium salts of lignin obtained from wasteliquors of the sulphate pulp process, which comprisesreacting the saidmaterial under pressure with hydrogen in an aqueous alkaline medium, ata temperature of the order of 250 C. to 420 C., the

introduction pressure of the hydrogen ranging I from 30 to 120atmospheres and separating the reaction products by distillation.

3. A non-catalytic process for the hydrogenation of a material selectedfrom the group consisting of sodium salts of lignin obtained from wasteliquors of the sulphite pulp process and sodium salts of lignin obtainedfrom waste liquors oi the sulphate pulp process, which comprisesreacting the said material under pressure with hydrogen in an aqueousalkaline medium, at a temperature of the order oi. 250 C. to 420 C., theintroduction pressure of the hydrogen ranging from 30 to atmospheres andrecovering the phenols and cyclic alcohols produced.

4. A non-catalytic process for the hydrogenation of sodium salts oflignin obtained from waste liquors of the sulphite pulp process, whichcomprises reacting the sodium sulphite of lignin under pressure withhydrogen in an aqueous alkaline medium, at a temperature of the order of250 C. to 420 C., the introduction pressure of the hydrogen ranging from30 to 120 atmospheres and recovering the phenols and cyclic alcoholsproduced,

5. A non-catalytic process for the hydrogenation of sodium salts oflignin obtained from waste liquors of the sulphate pulp process, whichcomprises reacting the sodium sulphate of lignin under pressure withhydrogen in an aqueous alka-. line medium, at a temperature of the orderof 250 C. to 420 0., the introduction pressure ofv the hydrogen rangingfrom 30 to 120 atmospheres and recovering the phenols and cyclicalcohols produced.

7 6. A process for the production 01' valuable products from a materialselected from the group consisting of sodium salts of lignin obtainedfrom waste liquors of the sulphite pulp process and sodium salts oflignin obtained from waste liquors or the sulphate pulp process, whichconsists in reacting the said material under pressure with hydrogen inan aqueous alkaline medium, at a temperature of the order of 250 C. to420 C., the introduction pressure of the hydrogen ranging from 30 to f20atmospheres and recovering the phenols and cyclic alcohols produced.

KARL FREUDEN'BERG.

WILLY mu'rscn.

